1. Technical Field
The present invention relates to a marker processing method, a marker processing device, a marker, an object having a marker, and a marker processing program.
2. Related Art
As a method of detecting a marker out of an image obtained by shooting an object attached with the marker there are known a method of detecting a symmetrical property of the shape and a method of detecting a combination of colors.
As a method of detecting a symmetrical property of a shape, there is proposed a method of detecting a two-dimensional code having a positioning symbol. The positioning symbol is disposed at a predetermined position, and the location and the rotational angle of the two-dimensional code can be obtained using the positioning symbol detected in the image thus shot (see, e.g., JP-A-7-254037 (Document 1)).
As a method of detecting a combination of colors, there is proposed a method of detecting a hue region entirely surrounded by a different hue region as a marker. The two hue regions used as a marker are previously provided with an identification number for each combination of colors. Therefore, a hue image is extracted from the shot image, and then a variation pattern in the hue is searched by scanning from the hue image thus extracted. By detecting the region, which can be expected to be the marker, using the hue search described above, and then determining whether or not the variation pattern of the hue thus detected matches the predetermined combination, the marker is detected (see, e.g., JP-A-2005-309717 (Document 2)).
However, according to the method of detecting the symmetrical property of the shape using the technology described above, since the positioning symbol, in which a ratio of dark and bright periods is set as dark:bright:dark:bright:dark=1:1:3:1:1 as shown in FIG. 2, is detected by scanning, there arises a problem that the detectable range of the symbol, which is rotated or tilted, becomes narrower depending on the scanning interval. Further, since a high symmetrical property is required for the marker itself in order to cope with the cases in which the scanning line for detecting the marker traverses the marker in various directions, which problematically causes restriction on creating a number of markers. Further, since it is only required that the dark and bright periods have the ratio of 1:1:3:1:1, and there is basically no limitation on the absolute periods, there arises a problem that the marker detection side is required to cope with the period variation due to the size of the marker. Further, since the black/white inversion period is used as the marker, determination of the period becomes difficult when noise is mixed into the input image. Therefore, there arises a problem that some measure against the noise becomes necessary.
In other words, the technology of the Document 1 has a problem that the marker detection depends on the posture (position, rotation, or tilt) of the marker, depends on the size of the marker, and is further influenced significantly by the noise in the image.
Further, in the method of detecting a color combination according to the technology described above, it is required to perform the data processing with an amount roughly three times as large as that in the case of using a monochrome image. Therefore, there arises a problem that it is required to reduce the resolution of the image or to reduce the frame rate when capturing the image in order for achieving the amount of processing equivalent to that in the monochrome image. Further, since the hue information in the shot image is significantly influenced by illumination conditions and so on, and is further influenced significantly by the white balance and so on of the camera used for shooting, there arises a problem that some countermeasures against these factors become necessary. Further, since the pigment or the color material in the material constituting the marker to be used varies across the ages, there arises a problem that some countermeasures against the aging become necessary.